public class Test03 {
    public int mySqrt(int x) {
        if(x < 1) return 0;
        long left = 1 , right = x;
        while(left < right){
            long mid = left + (right - left + 1) / 2;
            if (mid * mid <= x) left = mid ;
            else right = mid - 1;
        }
        return (int)left;

    }
}
